1. Field of the Invention
The present invention relates to a closed-type compressor to be included in a refrigerating cycle of a refrigerator or the like and more particularly to a reciprocating and closed-type compressor having a compressing machine provided with sliding portions improved in a wear resistance.
2. Description of the Prior Art
A refrigerator or cold storage, a refrigerating unit such as a refrigerating showcase and an air conditioner for cooling and heating a room is incorporated with a refrigerating cycle therein. The refrigerating cycle includes a compressor which is a closed-type compressing machine driven by an electric motor. The closed-type compressor compresses a compressor refrigerant to raise a temperature and a pressure of the compressor refrigerant which is then discharged into the refrigerating cycle.
A conventional closed-type compressor uses, as a compressor refrigerant, CFC (chlorofluorocarbon) 12 (hereinafter called "R12") or HCFC (hydrochlorofluorocarbon) 22 (hereinafter called "R22"), and as a lubricating oil, a naphthene type or paraffin type mineral oil is used. The compressor refrigerants and the lubricating oils are selected in consideration of a temperature, at which the compressor is used, a material of a sliding member, a capacity of a cylinder and so forth.
However, the refrigerant R12 is chemically stable in the atmosphere and there is, accordingly, a risk of destroying the ozone layer. Therefore, it is a specific fleon which must be regulated. On the other hand, the refrigerant R22 is a designated fleon because it can easily be decomposed in the atmosphere and its force for destroying the ozone layer is limited. However, it somewhat destroys the ozone layer and, therefore, a compressor refrigerant in place of the specific fleon and the designated fleon has been desired.
Recently, as an alternative fleon for use in place of the specific fleon and the designated fleon, refrigerant R134a, which is a HFC refrigerant that does not destroy the ozone layer, has been developed. The refrigerant R134a has characteristics as the refrigerant like R22, which is a HCC refrigerant.
If refrigerant R134a, which is the HFC refrigerant, is used as the compressor refrigerant to operate the closed-type compressor, the compatibility with the HFC refrigerant is unsatisfactory in a case where a mineral oil is used as the lubricating oil. Therefore, an ester oil has been investigated to be used as a lubricating oil that exhibits excellent compatibility with the refrigerant R134a.
If the refrigerant R134a, which is the HFC refrigerant, is used as the compressor refrigerant for the closed-type compressor and the ester oil exhibiting excellent compatibility with the refrigerant R134a is used, sliding portions or members of the compressing machine accommodated in a closed casing are worn excessively. Therefore, it is desired for the sliding portions to have excellent wear resistance property. The term "sliding portion" used herein means a portion at which two members of the compressing machine are slid with each other.
The conventional closed-type compressor of a type employing the reciprocating-type compressing machine has an arrangement that the sliding portions are made of cast iron or carbon steel, and the sliding portions, on which relatively high load and heavy duty act, are subjected to surface treatment such as a nitriding treatment to improve the surface hardness. Furthermore, the cast-iron cylinder for sliding a piston is subjected to precise finishing work such as honing to cause the sliding to be performed smoothly.
Even if the foregoing measurements are taken, the use of the refrigerant R134a containing no chlorine as the compressor refrigerant and the use of the ester-type oil as the lubricating oil for the closed-type compressor cause excessive wear and damage to occur in the sliding portions of the compressing machine, in particular, the sliding portions between the cylinder and the piston and between a small-diameter end ball portion of the connection rod and a piston spherical seat portion. Therefore, there arises a problem in maintaining the performance of the compressor and the reliability thereof.